Printing telegraph system



Jun 1, 1937. I E, M, T N 2,082,075

PRINTING TELEGRAPH SYSTEM Filed Nov. 10. 1953 2 Sheets-Sheet 1 //V VE N 7' OR By M MOWTO/V ATTORNEY Jun 1, 1937;

' E. M. MOWTON PRINTING TELEGRAPH SYSTEM Filed Nov. 10, 1933 2 Sheets-Sheet 2 Has 3/6 g g .209 308 L 5? (,6

INVENTOR E. M MOWTON Y Patented June 1, 1937 UNITED STATES PATENT OFFIQE PRINTING TELEGRAPH SYSTEM Edward M. Mowton, Yonkers, N. Y., assignor to American Telephone and Telegraph Company, a corporation of New York Application November 10, 1933, Serial No. 697,509 22 Claims. (01. 178-4.1)

This invention relates to communication sysa contact which is so arranged as to short-cirtems, and more particularly to printing telegraph cult a resistance also at the receiving station. systems in which it is desired to obtain a check This resistance is in series with a control line upon the operability of receiving teletypewriters. leading from the receiving station to the send- It is an object of this invention to provide an ing station.

arrangement for warning an operator at a send- A differential polar relay located at the sending printing telegraph station of the improper ing station has one of its windings in series with functioning of apparatus at either the sending the control line and is normally balanced so that printing telegraph station or a receiving printits armature is in a certain position. When the ing telegraph station connected to the sending contact at the receiving station is operated by 10 station. the reception at the receiving station of the pre- In printing telegraph systems, there is often assigned signal transmitted over the message the possibility that an operator might send mes transmission line by the sending teletypewriter, sages to another station at which the printer mothe resistance is shunted out of the control line.

tor could not be started due, perhaps, to some This causes the balance of the differential polar 15 local circuit trouble. Normally, the sending oprelay at the sending station to be disrupted thereerator would have no immediate knowledge of by causing its armature to go to its opposite pcthe fact that these messages had not been resition. In this opposite position, the armature ceived and would keep on sending messages. of the difierential polar relay closes a path for 0 Since these messages would not be printed by the Current t light a Signal l p at h Sending receiving teletypewriter, their transmission would station. be a waste of time, money and energy. There is When the operator at the sending station also the possibility that confusion might result transmits another signa Which may be y from the sending operator believing that the character, over the message transmission line,

messages had been received, especially if the mesthe contact at the receiving station is put back 25 sages were orders todo something immediately, into its normal position thereby putting the resuch as to buy or sell stock. In order to obviate sistance in series with the control line again. this undesirable contingency, it is necessary to This restores the balance of the difierential polar employ some arrangement for informing a sendrelay at the sending station thereby causing its ing operator when a receiving station is not funcarmature to go back to its first position. In so 30 tioning properly. doing, the armature opens the energizing circuit The object of this invention is to provide such for the signal lamp and causes the lamp to go an arrangement, but this invention s n eout. Failure of the lamp to light or to go out at stricted to p g telegraph Systems as t may be the proper time indicates to the sending operapp y Communication Sy in general. tor that there is something wrong with the ap However, for the p p Of illustration, this paratus at either the sending station or the revention will be described chiefly with reference to ceiving st ti n,

its application to a, telegraph system. The arrangement described above nay be mod- Heretofore, in printing telegraph Systems, it ified to have the resistance normally short-cir- 40 has been common practice to install apparatus at ut and t be put t th t l line i 40 a receiving station for transmitting messages response to the reception at the receiving station received at that station back to the sending staf the preassigned signal transmitted by t t o e objections to this procedure are that sending teletypewriter. According to this modi-.

it cannot be readily applied to any Printing tele' fication, the insertion of the resistance into the graph system and that it requires additional control line would throw the differential polar Pamtlls which 1S Y relay out of balance. Then, the transmission of In accordance with thls mventlon slmple and any other signal would short-circuit the resistinexpensive arrangement is provided which may ance thereby restoring the balance f the readily be apptied t0 any Priming i Sysferential polar relay. Another modification of 59 tam 9 the operatlon appmttus i this invention provides for two-way use of this a receiving printing telegraph statlon. With this t Still nothe modifica arrangement, whenever a sending operator wishes checkmg f g t a r o tlon of this invention enables this checking opto know if apparatus ata receiving prmting teleb f d b twe n two graph station is functioning properly, the operafltlon to e per Orme e e S q .5 erator transmits a preassigned signal composed W are connected by transmlsslon of significant current variations over the mes- 11116 Instead of two transmlssmn hnes' sage transmission line to the receiving station by The invention W111 be better understood from means of her sending teletypewriter. In transthe following detailed description with reference mitting this signal, the sending teletypewriter to the accompanying drawings in which:

60 causes the operation at the receiving station of F gure 1 illustrates the broad principle of the 6 invention which may be applied to any communication system in general;

Fig. 2 represents the invention applied for one- Way use with two transmission lines;

Fig. 3 shows how the invention may be applied for two-way use with two transmission lines; and

Fig. 4 represents the invention applied for twoway use with only one transmission line.

In Fig. 1 is shown an arrangement by means of which an operat r at a communication station A can control the operation of electrically operated rotating or reciprocating equipment at another communication station E and obtain an indication which will indicate whether or not the controlled equipment at station B is functioning properly.

When the operator at station A wishes to put the equipment at station B in operation, she closes the power switch it! thereby starting motorgenerator I62 which supplies a direct current voltage between the ground and the common point of the windings a and b of the differential polar relay its. Current from the motor-generator 962 is supplied with two paths. One path leads from motor-generator 9532 through the biasing winding 2? of the differential polar relay m3 and then through the resistance H535 to ground. The other path leads from motor-generator Hi2 through the line winding a of the differential polar relay E83, over the line L to the control relay I86 at station B. From the control relay M5, the current passes through contact I it to ground. The magnitude and direction of the line current flowing through the winding 0. of the relay E93 are such as to overcome the effect of the biasing current flowing through the winding b, thus preventing the relay 563 from being operated by the biasing current. Since the relay M33 is not operated, its armature remains unoperated thereby holding open the circuit passing through signal lamp l M.

The line current flowing through the winding of the control relay m5 causes it to operate its armature thereby closing a path from the volt alternating current source at station E to any controlled equipment, such as the motor 509. When the controlled equipment (motor 899) is in operation, some interrupting device, such as the cam its, is also set in operation and opens and closes the contacts Hi] periodically.

When the contacts HE; open, the resistance ii? is placed in the line circuit in series with winding a of the differential polar relay N33. The addition of the resistance ill! to the line circuit reduces the line current sufliciently to allow the current through the biasing winding b of relay 93 to predominate and to cause relay I53 to operate its armature. When relay 2% operates, the circuit through the signal lamp iii l is closed thereby causing the lamp N34 to light. However, the line current still remains large enough to keep the control relay liiE operated.

When the cam we allows the contacts lie to close, the resistance H3! is short-circuited and the current through the line winding a of relay I03 is increased to its former value. This will cause relay ms to release its armature thereby opening the circuit through lamp Iii-i and causing lamp HM to be extinguished.

Thus, the operation of the cam 28, which is dependent on the operation of the controlled equipment (motor E69), causes a periodic signal to be given to the operator at station A indicating that the controlled equipment at station E is functioning properly. Failure of lamp its to light or go out at the proper time indicates to the operator at station A that the equipment at station B is not functioning properly. The invention is not limited to the use of a signal lamp for informing the operator. Any other type of an alarm device could be used, such as a bell or buzzer.

To shut down the equipment at station B, the operator at station A opens the power switch IUI which stops the motor-generator I 62. When the motor-generator m2 stops, no current will be supplied to the winding of the control relay H16 which consequently releases. Upon the release of relay tilt, the path leading from the 110 volt alternating current power supply to the controlled equipment (motor are) is opened thereby causing the controlled equipment to stop operating.

The circuit shown in Fig. 2 is essentially. that of Fig. 1 applied to a printing telegraph circuit. At the sending station A is shown the sending teletypewriter 2M which operates to transmit significant current variations over the message transmission line L1 to the receiving teletype- Writer 2E5 at the receiving station. B.

When the operator at station A wishes to communicate with the operator at station B, she closes the power switch 20! which closes a path from power source 222 to the printer motor 2M and the motor-generator 292 and starts them in operation. The motor-generator 262 causes current to flow out over line L1 and also in two paths similar to those mentioned in the description of the operation of the circuit shown in Fig. 1. One of these two paths leads from motor-generator 2532, through the biasing winding b of the differential polar relay 203, and then through the resistance 285 to ground. The other path leads from motor-generator 2&2 through the line winding a of relay 2&3, over the control line L2, through the winding of the control relay 296, and then through resistance 2!]? to ground.

The passage of current through the winding of control relay 2% causes it to operate its armature and thereby connect power from source 223 to the receiving teletypewriter motor 289. Also, the passage of current through the line winding 0!. of the differential polar relay 203 tends to cause it to operate. However, the magnitude and direction of the biasing current flowing through the winding b of relay EH03 is such as to oppose the effect of the current flowing through winding a1 and prevents relay 2% from operating.

When the operator at sending station A wishes to know if the teletypewriter apparatus at station B is functioning properly, she transmits, by means of the sending printer 2i i, a preassigned signal, such as a carriage return signal, over the message transmission line L1. When this signal is received by the receiving teletypewriter 2 l 5, the carriage 2E6 of the receiving teletypewriter 2E5 moves to its carriage return position. In so doing, a contact arm 2% on the carriage 2H6 causes the contacts Eli] to close. When contacts 2H] close, they short-circuit resistance 2%? and shunt it out of control line L2. With the resistance 221'! out of line L2, the line current flowing through the winding a of relay 2&3 increases sufficiently to overcome the efiect of the biasing current flowing through the winding b and to cause relay 2t3 to operate its armature. The operation of the armature of relay 253 closes the circuit through signal lamp 2534 thereby lighting lamp 2%.

The operator at station A now transmits any other signal over the line L1. When this signal is received by the receiving teletypewriter M5 at station B, it causes the carriage 255 of the tele typewriter 2E5 to move from its carriage return position. This opens the contacts 2I0 thereby removing the short-circuit from the resistance 201 and causing the control line current to drop to its original value. The balance is now restored to relay 203 which releases its armature and thereby opens the circuit through signal lamp 204 causing lamp 204 to' be extinguished. The lighting and extinguishing of the signal lamp 204 at the proper times indicates to the operator at station A that the teletypewriter apparatus at station B is functioning properly. It is to be understood that any other type of alarm device could be used instead of the signal lamp 204.

The functioning of the signal lamp alarm circuit of Fig. 1 differs from that of Fig. 2 in that resistance I01 in Fig. 1 is normally short-circuited whereas resistance 201 in Fig. 2 is normally in control line L2. The signal lamp I04 is lit when the contacts IIO, which short-circuit the resistance I01, are opened and the resistance I01 is put in the circuit. In Fig. 2 the signal lamp 204 is lit when the contacts 2I0 are closed to shortcircuit resistance 201. Attention is called to the fact that either method of controlling the operation of the signal lamp is satisfactory and that the methods may be interchanged if desired. It the method of Fig. 1 is used in Fig. 2, the contacts 2I0 must be arranged so that they are opened by the contact arm 208 when the printer carriage 2I6 is in the carriage return position.

In Fig. 3 the stations A and B are arranged so that they may be used for either sending or receiving depending upon the position of the keys 320 and 32I. With the keys 320 and 32I in their normal position, as shown in Fig. 3, the teletypewriter apparatus of both stations A and B is in the receiving position. Stations A and B are identical in their manner of operation and differ only in that station A is operated from a direct current source 322 while station B is operated from an alternating current source 323.

When the operator at station A wishes to communicate with the operator at station B, she operates the key 320 which applies the direct current source 322 to the direct current teletypewriter motor 3I4 through the contacts I and 2 of key 320. The direct current source 322 also sends current through the contacts 4 and 5 of key 320 through the biasing winding b of the differential polar relay 303, through resistance 305, and then to ground. Current from the direct current source 322 also passes through the line winding a of the differential polar relay 303, through resistance 324, out over the control line L2, through resistance 325, and then to winding a of the differential polar relay 326 where it is provided with two paths. One path leads through winding b, resistance 301, and then to ground. The other path leads through contacts 2 and 3 of key 32I, to control relay 306, and then to ground. The passage of current through the winding of the control relay 306 causes it to operate its armature. When relay 306 operates its armature, it closes a path from the alternating current source 323 to both the motor-generator 3I3 and the receiving teletypewriter motor 309. The generator of motor-generator 3I3 is connected so as to aid rather than oppose battery 322.

Then, as was explained in the description of the circuit of Fig. 2, the operator at station A transmits a preassigned signal, such as a carriage return signal, over the message transmission line L1 by means of her sending teletypewriter 3II. When this carriage return signal is received by the receiving teletypewriter 3I5 at station B, it causes the carriage 3I6 of the receiving teletypewriter 3I5 to move to the carriage return position. With the carriage 3I6 in this position, the contact arm 308 is made to close the contacts 3I0.

When contacts 3I0 close, they short-circuit the resistance 325 which causes an increase of the current in the control circuit over control line L2 to a value equal to the current in the Winding b. Since relays 303 and 326 are adjusted to hold their armatures on either contact until differential current in their windings causes them to operate their armatures to the other contact, lamp 304 will not be lit at this time.

At the same time, the carriage 336 of the sending teletypewriter 3 at station A will move to its carriage return position and will cause its contact arm 338 to close contacts 330. When contacts 330 close, they short-circuit the resist ance 324 which causes a further increase of the current in control line L2. This further increase of the current in control line L2 causes the differential polar relay 303 to operate. As was the case with the apparatus shown in Fig. 2, this procedure causes the lighting of the signal lamp 304.

Incase one of the teletypewriters 3H and 3I5 is not functioning properly, its corresponding contacts (330 or 3I0, respectively) will not be closed. Consequently, the current in control line L2 will not be increased sufficiently to cause the differential relay 303 to operate. Thus, lamp 304 will not be lit thereby indicating to the operator at station A that the teletypewriter apparatus at either station A or B is not functioning properly.

The above description applies to Fig. 3. Contacts 3I0'and 330 are normally open when operation is commenced. If these contacts (3I0 and 330) are closed when operation is commenced, lamp 304 will light and remain lit upon failure of either teletypewriter 3I2 or 3I5 to function.

If lamp 304 lights, thereby indicating that the teletypewriter apparatus at both stations A and B is functioning properly, the operator at station A then sends any other signal over the message transmission line L1. This causes the carriage 356 of the receiving printer 3I5 to move from its carriage return position thereby opening the contacts 3I0. In the same way, contacts 330 will also be opened. When both contacts 3I0 and 330 open, the line current will be restored to its normal value. This will cause relay 303 to release thereby extinguishing the signal lamp 304. The extinguishing of lamp 304 also indicates to the operator at station A that the teletypewriter apparatus at both stations A and B is performing its functions properly.

After the desired communication with station B has been completed, the operator at station A should move key 320 back to its normal position. This will disconnect the direct current source 322 and will restore both stations A and B to their normal receiving condition.

When the operator at station B wishes to communicate with the operator at station A, she operates'the key 32I which applies the alternating current source 323 through the contacts 4 and 5 of key 32I to the alternating current teletypewriter motor 309 and to the motor-generator 3I3. When the motor-generator 3I3 operates, current is sent through contacts I and 2 of key 32I, the a Winding of diiferential polar relay 326, through resistance 325, and out over line L2 to station A. At station A, the line current passes through resistance 324, the a Winding of differential polar relay contacts 4 and 3 of key 328, the winding of control relay 346, and then to ground.

The operator at station B then goes through the same procedure with her sending teletypewriter has just been described above for the operator at station A. If both the receiving teletypewriters i 2 at station A and the sending teletypewriter 53!; at station B are functioning properly, the signal lamp 334 will operate in the manner described above for lamp 3%, thereby indicating to the operator at station B that the teletypewriter apparatus at both stations A and B is -Jnctioning properly.

The circuit shown in Fig. e performs the same functions over the one line L as the circuit shown in 3 performs over the two lines L1 and L2. When the operator at station A Wishes to communicate with the operator at station B, she operates the key When key M9 is operated, power from the ClliEC G current source 422 is supplied to the direct current teletypewriter motor Mt through contacts i and 2 of key 426. Also, current from direct current source 322 will pass through contacts t and ii of key :26, the biasing winding Z of the differential polar relay 403, resistance 65, and then to ground. Likewise, current from direct current source 622 will pass through the winding of relay 483, resistance mt, the sending teletypewriter 4H, the receiving teietypewriter M2, and then out over line L to station B.

At station B, the line current passes through the receiving teletypewriter M5, the sending teletypewriter 339, resistance 125, and then through the a winding of differential polar relay 426. From here it passes through contacts 2 and 3 of key 42! to the control relay 4% and then to ground. l'his will cause control relay iilfi to operate thereby putting ground on the relay do! which, in turn, applies power from the alternating current source 123 to the alternating current teletypewri'ter motor toe and the motorgenerator H3. Hou ever, the direct current circuit of the motor-generator H3 is kept open by the con tacts and 2 of key 52i. It is to be noted that relays and operate their armatures in the s. e manner as relays 3% and 326.

In the manner that has been explained in the description of the circuit shown in Fig. 3, the operator at station A will transmit a carriage return signal over the line L which, if the teletypewriter apparatus at both stations A and B is functioning properly, will cause the contacts 436 and M9 to operated. The operation of contacts 638 and i will increase the current passing through relay to an amount sufi'icient to operate it thereby lighting signal lamp M l.

It is recognized that, it signals are being transmitted during the period that contacts iiii and 4% are clos-em, the armature of the differential polar relay iil l may be chattering. This contingency might prevent lamp sea from lighting. To prevent it is advisable for the operator at station A to wait, after sending a carriage return signal, until lamp has had time to operate befcre proceeding with the transmission of messages.

When any other signal is sent from station A to station B, the lamp its wiil be extinguished in the manner described for the circuit shown in Fig. 3. When key iiili is restored to its normal position by the operator at station A, the apparatus at both stations A and B will be restored to the normal receiving condition.

When the operator at station E wishes to communicate with the operator at station A, she will operate the key Mi. This will apply current from the alternating current source 423 through the alternating current teletypewriter motor 469 and the motor generator H3. The motor-generator tit will now send current through the contacts I and 2 of key 12i and through the windings of diiierential polar relays E26 and M3. This will cause control relay 445 to operate which, in turn, will cause the operation of relay 459. When relay 45c operates, it closes a path from direct current source 422, through the armature of relay 59, to the direct current teletypewriter motor 4M and then to ground.

The operator at station B, using the procedure described above for the operator at station A, will then test the teletypewriter apparatus at both stations A and B to see if the signal lamp 434 will be lighted and extinguished as required to indicate that the teletypewriter apparatus of both stations A and B is functioning properly.

Attention is called to the fact that the control relays 446 and tilt and also relays 50 and 455i are of the slow-to-release type. The purpose of this is to prevent unintentional operation of these relays due to momentary interruptions of the Current in line L during the transmission of message signal impulses.

The arrangements shown in the drawings and described above are illustrative of the operation of the invention and will serve to assist in interpreting the claims. The claims are not to be restricted to the precise construction described above, but are intended to includeall changes and modifications employing the principles and features of operation of the invention.

What is claimed is:

i. A communication system comprising in combination a first teletypewriter, a second teletype- Writer, a first transmission line having a ground return for connecting the two teletypewriters for the transmission of significant current variations, a second transmission line having a ground return for connecting the two teletypewriters,andinstrumentalities operating over the second transmission line for obtaining a check upon the capability of the second teletypewriter to correctly receive the current variations transmitted to it over the first transmission line by the first teletypewriter.

2. A printing telegraph system comprising in combination a first printing telegraph instrument, a second printing telegraph instrument, a first transmission line having a ground return for connecting the two instruments for the trans mission of significant current variations, a. second transmission line having a ground return for connecting the two instruments, and instrumentalities operating over the second transmission line for obtaining a check upon the capability of the second instrument to correctly receive the current variations transmitted to it over the first transmission line by the first instrument, said instrumentalities including an alarm device connected to the second transmission line and located near the first printing telegraph instrument for warning the operator of that instrument of the improper functioning of either instrument.

3. A communication system comprising in combination a first station having a teletypewriter, a second station having a teletypewriter, a transmission line connecting the two teletypewriters,

instrumentalities for informing the operator at the first station of the improper functioning of the teletypewriter at the second station, said instrumentalities including an alarm device located at the first station, a circuit for operating the alarm device, said circuit extending from the first station to the second station, a relay located at the first station in series with the circuit for operating the alarm device, a resistance located at the second station in series with the circuit, and a contact at the second station for shunting the resistance out of the circuit.

4. A comunication system comprising in combination a first teletypewriter, a second teletypewriter, a first transmission line connecting the two teletypewriters for the transmission of significant current variations, a second transmission line connecting the two teletypewriters, instrumentalities operating over the second transmission line for obtaining a check upon the operability of each teletypewriter, said instrumentalities including an alarm device connected into the second transmission line, a polar relay connected into the second transmission line for operating the alarm device, a resistance connected into the second transmission line, and a contact for shunte ing the resistance out of the second transmission line, said contact being operated in response to the transmission and reception of a particular signal transmitted by the first teletypewriter over the first transmission line to the second teletypewriter.

5. In a communication system having two communication stations connected by a transmission line, instrumentalities for enabling an operator at one station to control the operation of electrically operated reciprocating equipment at the other station in response to the application of current to the transmission line, and signaling apparatus for indicating to the operator at the first mentioned station whether the controlled equipment at the second mentioned station is functioning properly, said signaling apparatus.including a rotating cam located at the second station for periodically varying the amount of current in the line and a differential relay located at the first station for periodically opening and closing a circuit for operating an indicating device also at the first station in response to the periodic variations in the amount of the line current.

6. A two-way teletypewriter system comprising in combination two teletypewriter stations connected by two telegraph lines, instrumentalities at each station for enabling an operator at either station to control the operation of a teletypewriter located at the other station, and signaling apparatus at each station for indicating to an operator at one station whether the teletypewriter apparatus at the other station is functioning properly, said signaling apparatus being putinto operation in response to the transmission and reception of a particular combination of significant current variations and being taken out of operation in response to the transmission and reception of any other combination of significant current variations.

7. A teletypewriter system comprising in combination a plurality of teletypewriter stations connected by a plurality of telegraph lines, instrumentalities at one station for enablingan operator at that station to control the operation of a teletypewriter located at another station, and signaling apparatus for enabling that operator to obtain an'indication which will indicate whether the controlled teletypewriter is functioning properly, said signaling apparatus being put into operation in response to the transmission and reception of a particular combination of significant current variations and being taken out of operation in response to the transmission and reception of a different combination of signlficant current variations.

8. A teletypewriter system having two teletypewriter stations connected by a telegraph line, instrumentalities for enabling an operator at one station to control the operation of a teletypewriter located at the other station, and signaling apparatus for indicating to said operator whether the controlled teletypewriter is functioning properly, said signaling apparatus including an indicating device located at the station where the operator is, an electroresponsive device for operating the indicating device, said electroresponsive device being connected into the telegraph line and located at the station where the operator is, a resistance connected into the telegraph line and located at the station where the controlled teletypewriter is, and a contact for shunting the resistance into and out of the telegraph line, said contact being connected into the telegraph line and located at the station where the controlled teletypewriter is.

9. A printing telegraph system having two printing telegraph stations connected by a telegraph line, an indicating device located at one station, instrumentalities for operating the indicating device, said instrumentalities including a relay connected into the telegraph line and responsive to variations in the amount of current in the telegraph line, a resistance located at the other station and connected into the telegraph line, and a contact for varying the amount of current in the line by shunting the resistance into and out of the line.

10. A teletypewriter system comprising in combination two teletypewriter stations each having a teletypewriter and connected by a telegraph line, an indicating device located at one station, instrumentalities for operating the indicating device, said instrumentalities including a relay connected into the telegraph line and responsive to variations in the amount of current in the line, a resistance located at the other station and connected into the telegraph line, a contact for varying the amount of current in the line by shunting the resistance into and out of the telegraph line, said contact being opened and closed by different positions of the carriage of the teletypewriter located at the same station where the resistance is located.

11. A teletypewriter system comprising in combination a teletypewriter station having a teletypewriter having a direct current motor and a source of direct current for operating that motor, a second teletypewriter station having a teletypewriter having an alternating current motor and a source of alternating current for operating that motor, a telegraph line for conmeeting the two teletypewriters, an alarm device connected to one teletypewriter for indicating to an operator of that teletypewriter the improper functioning of the other teletypewriter, and instrumentalities for operating the alarm device.

12. A teletypewriter system comprising in combination a teletypewriter station having a teletypewriter having a direct current motor and a source of direct current for operating that motor, a second teletypewriter station having a teletypewriter having an alternating current motor and a source of alternating current for operating that motor, a telegraph line for connecting the two teletypewriters, an alarm device connected to one teletypewriter for indicating to an operator of that teletypewriter the improper functioning of either teletypewriter, and instrumentalities for operating the alarm device.

13. In a communication system having two communication stations, apparatus at one station operated by direct current, apparatus at the other station operated by alternating current, a communication line connecting the apparatus at one station to the apparatus at the other station, instrumentalities at one station for controlling the operation of the apparatus at the other station, signaling apparatus for indicating whether the controlled apparatus is functioning properly, and instrumentalities for operating the signaling apparatus.

14. A teletypewriter system comprising in combination a communication line, a first teletypewriter station connected to the line, a second teletypewriter station also connected to the line, an indicating device located at the first station for indicating to an operator at that station that the teletypewriter at the second station is functioning properly, and instrumentalities for operating the indicating device, said instrumentalities including a contact adapted to be operated by one of the teletypewriters.

15. A teletypewriter system comprising in combination a telegraph line, a first teletypewriter station connected to one end of the line, a second teletypewriter station connected to another end of the line, each of the teletypewriters at said teletypewriter stations having a movable carriage, an indicating device located at the first station for warning an operator at that station of the improper functioning of either teletypewriter, and instrumentalities for operating the indicating device, said instrumentalities includ ing a contact located at each station, each contact being adapted to be operated by the carriage of the teletypewriter at the same station.

16. A teletypewriter system comprising in combination a telegraph line, a first teletypewriter station connectable to one end of the line,

; a second teletypewriter station connectable to another end of the line, each of the teletypewriters at said teletypewriter stations having a movable carriage, an indicating device located at the first teletypewriter station for indicating to an operator at that station the improper functioning of a teletypewriter, and instrumentalities for operating the indicating device in response to a variation in the amount of current flowing over the line, said current variation being efiected by a certain movement of the carriage of a teletypewriter.

17. A teletypewriter system having a first teletypewriter station, a second teletypewriter station, a communication line connecting the two stations, said line normally having current of a certain amount passing over it, a circuit for energizing and operating an indicating device at the first station, said circuit being normally open, control means for reducing the line current to an amount smaller than its normal amount but more than zero, and an instrumentality responive to the reduction in line current for closing said normally open circuit.

18. A teletypewriter system having a first teletypewriter station, a second teletypewriter station having a teletypewriter with a movable carriage, a communication line connecting the two stations, said line normally having current of a certain amount passing over it, a circuit for energizing and operating an indicating device at the first station, said circuit being normally open, control means operable by the carriage of the teletypewriter at the second station for reducing the line current to an amount smaller than its normal amount but more than zero, and an instrumentality responsive to the reduction in line current for closing said normally open circuit.

19. A teletypewriter system having a first teletypewriter station, a second teletypewriter station, a communication line connecting the two stations, said line normally having current of a certain amount passing over it, a circuit for energizing and operating an indicating device at the first station, said circuit being normally open, control means for reducing the line current to an amount smaller than its normal amount but more than zero, and a differential relay at the first station responsive to the reduction in the line current for closing said normally open circuit.

20. A transmission system having two communication stations, instrumentalities for enabling an operator at one station to control the operation of electrically operated rotating equipment at the other station, an indicating device for indicating to an operator at the first station whether the controlled equipment at the second station is functioning properly, a circuit for operating the indicating device, a rotatable cam located at the second station, and an instrumen tality for continuously rotating the cam during the period of operation of the controlled rotating equipment, the rotation of said cam being adapt ed to periodically effect the operation of said indicating device.

21. A teletypewriter system having a first teletypewriter station, a second teletypewriter station, a communication line connecting the two stations, each of said stations having a teletypewriter motor, motor starting means at the first station for starting the motors at both stations, a normally unoperated indicating device at the first station, a source of line current, and means for applying it to the line, instrumentalities for reducing the line current to an amount less than its normal amount but more than zero, and a normally unoperated relay for controlling the operation of the indicating device, said relay being adapted to operate in response to the reduction in the line current to operate the indicating device.

22. A communication system having a first communication station, a second communication station, a communication line for connecting the two stations for the transmission of messages normally unoperated apparatus at the second station, control means at the first station for putting said apparatus into operation, a normally unoperated indicating device at the first station for indicating that said apparatus is operating, a resistance located at the second station and connected into the line, and an instrumentality at the second station for varying the resistance of the line by short circuiting said resistance at intervals during the transmission of a message, said indicating device being adapted to operate in response to the variations in the line resistance.

EDWARD M. MOWTON. 

